A few weeks back I was looking at the Gracenotes CD Database and other alternative sites which perform a similar task.
When I searched in Wikipedia it gave info about how Gracenotes works and it is a pretty simple analysis based only on the number and length (time) of the tracks on a CD. It assumes that no two CDs will contain the same number of tracks with matching lengths in the same order. Obviously it is possible, as in the case of the two Scottish CDs, for two CDs to have matching track lengths and therefore give an incorrect identification. BLICKY
Other databases may use a different method of differentiation.
Further reading here http://en.wikipedia.org/wiki/Acoustic_fingerprint

Quack!
GtD.